[kriswd40]

I have a 2001 Mariah Diablo with a 4.3 litre MerCruiser engine.

The very last time last summer I tried to take it out, it started fine and then just after I left the dock, it stalled. The engine would crank but not turn over. I took it home and tried a few days later while it was parked in my driveway (with the hose attached) and it ran fine and stayed running. I didn't have another chance to take it out until just yesterday.

I changed the plugs and wires before the season started and run it in my driveway again. Started up fine, stayed running, no issues. Started up better than it has since I've owned it actually, I think thanks to the new spark plugs, the old ones looked pretty worn. Got out on the lake and it ran great for about 20 minutes, then it started sputtering and stalled out. It wouldn't turn over again, I let it sit for 15 minutes or so and was able to get it to start again, but it was sputtering the entire time. The boat wouldn't move fast at all. It ran like this for a bit before stalling out again. I couldn't get it to turn over after that and got it towed in.

Just hoping for some advice as to what to check / fix here. I'm thinking I'll start with replacing the fuel filter but maybe there are other things to change too. If its bad gas, I'm not sure what I can do about that, as the tank is mostly full and I have no idea were I could put 20+ gallons of gas.

[Hudson River Steve]

When was the last time the fuel filter was changed? Sounds like you may have water in your fuel.

[kriswd40]

I changed it not at the end of last season, but the end of the season before.

Will it be obvious once I remove it if water is in it or not? I ordered two replacement fuel filters (one for now, one as a spare) that will be arriving Thursday. It would be nice if I could determine if this really is the problem without having to strand myself out on the lake again or annoying the neighbors by running the boat for a long time in the driveway, although maybe that's what I'll have to do.

[Hudson River Steve]

When you remove the fuel filter, dump the contents into a clear container (glass). Let it sit. If you have any water, you will see it at the bottom of the glass.

[kriswd40]

Thanks, I'll check that out hopefully when I get home.

[ChrisH]

Had similar issue on my 4.3 would just about tick over on idle . Any load would cause the engine to die. Turned out to be a bad connection on the fuel pump.

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[kriswd40]

Is there any trick to getting the old fuel filter off? I've even got one of those filter wrenches and the thing won't budge.

I'll look for some bad connections too, thanks.

[kriswd40]

Never mind, got it off. Hit it with a mallet some and then just had to turn really, really hard.

Letting it sit right now to see what, if anything, is in the gas.

[kriswd40]

I let what was in the fuel filter sit overnight and I didn't see any water in the jar. I'm not sure if that means that the fuel filter isn't the problem or not. I should be receiving the replacements today so maybe I'll run the boat in the yard for a while and see if it happens again.

I'm open to more suggestions in case that doesn't solve it.

[Hudson River Steve]

If there was water in the fuel filter you would have seen it in the bottom of the jar. So it sounds like you have eliminated that as a potential fault.
Is your engine carburated or fuel injected? I assume since it is a 2001 that it is injected. If fuel injected do you have a fuel pressure gage to monitor fuel pressure?
If you have low or no fuel pressure then what ChrisH mentioned could be your problem. You may have a loose connection in the fuel pump wiring, a bad fuel pump or a more common fault is a fuel pump relay that it on its way out. Check the fuel pressure, it should be around 40 psi or so. If it is good then perhaps your problem is ignition related.